Ascendonanus
|image = Ascendonanus restoration.png | image_caption = Restoration of A. nestleri | domain = Eukaryota | regnum = Animalia | phylum = Chordata | familia = Varanopidae | binomial_authority = Spindler et al., 2018 | genus = Ascendonanus | binomial = Ascendonanus nestleri }} Ascendonanus (meaning ″climbing dwarf″) is a varanopid pelycosaur from the Early Permian of Germany described in 2018.Frederik Spindler; Ralf Werneburg; Joerg W. Schneider; Ludwig Luthardt; Volker Annacker; Ronny Rößler (2018). "First arboreal 'pelycosaurs' (Synapsida: Varanopidae) from the early Permian Chemnitz Fossil Lagerstätte, SE Germany, with a review of varanopid phylogeny". PalZ. 92 (2): 315–364. It contains one species, Ascendonanus nestleri. The taxon is the earliest specialized arboreal tetrapod currently known, with strongly curved claws, short limbs, a slender, elongated trunk, and a long tail, similar to some modern tree-living lizards. It was about 40 cm long and would have preyed on insects and other small arthropods. The fossils of Ascendonanus include remains of skin, scales, scutes, bony ossicles, and body outlines, providing a unique record of integument from early synapsids and indicating that some of the oldest relatives of mammals had a scaly ″reptilian-type″ appearance. Remains of five individuals that were discovered in the Chemnitz petrified forest, an Early Permian tropical fossil forest preserved under the city of Chemnitz, Germany, from a Pompeii-like pyroclastic eruption 291 million years ago that buried the forest and created the Zeisigwald Tuff Horizon in the uppermost Leukersdorf Formation (late Sakmarian/early Artinskian transition stage). The specimens of Ascendonanus are stored at the Chemnitz Museum of Natural History (Museum für Naturkunde Chemnitz (MNC)). The type species name A. nestleri honors Knut Nestler, a long-time local supporter of the museum (deceased). The painstaking fossil preparation work was done at the Natural History Museum Castle Bertholdsburg (Naturhistorisches Museum Schloss Bertholdsburg) in Schleusingen, Germany. Description The fossils of Ascendonanus are strongly compacted and were split open as flattened counterslabs that revealed articulated partial or near complete skeletons with remains of soft tissue and some internal features. The bone material itself, however, often was not clearly preserved, making interpretation of some details more difficult. It is also not known if the skull is relatively flat or if it has a taller profile. The tip of the snout is not well preserved in any specimens and the end part of the long tail is missing. The specimens were CT scanned to reveal additional information. Based on the ossification of different bones, all individuals appear to be fully grown despite some differences in size. The specimen designated MNC-TA0924 was made the diagnostic holotype of Ascendonanus nestleri because it provides the clearest details of the skull. The most remarkable specimen (MNC-TA1045) preserves the clear body outline of nearly the entire animal on counterslabs, showing the thickness in life of the limbs and the neck, and the full covering of scales. Ascendonanus was about 40 cm long (but full tail length is not currently known) and is the smallest known member of the clade Varanopidae, a group of early synapsids that generally resembled the unrelated monitor lizards. Features that identify Ascendonanus as a ″pelycosaur″ grade synapsid and a member of the Varanopidae include a single lateral temporal opening (fenestra) in the skull, a ridge on the underside of the centra of the vertebrae, and enlarged blades on the ilium of the pelvis. The skull has a very large orbit but the sclerotic rings to support the eyeball are not ossified. Some specimens preserve dozens of tiny round dermal bones or ossicles that were embedded in the skin of the upper eyelid. Such eyelid ossicles are currently not known in any other amniotes, but have been found in some dissorophid temnospondyl amphibians, a non-amniote tetrapod group that is not closely related to synapsids. The eyelid ossicles in Ascendonanus may have evolved independently or may be an ancient feature retained from the earliest tetrapods. (Such eyelid ossicles are distinct from the rod-like dermal bones, called palpebral bones, that evolved above the eye socket in a number of later non-synapsid groups, including some ornithischian dinosaurs.) The pointed teeth are slender, without flattened cross-sections, serrations, or a cutting edge, and are are moderately recurved in the upper jaw and straighter in the lower jaw. Ascendonanus differs notably from other varanopids in its elongated trunk section, with 34 to 37 presacral vertebrae compared to 26 in most synapsids. It has a dense set of thin belly ribs or gastralia along the underside. The full length of its tail is not known based on current fossils, but the organ was longer than in other described varanopids and would have helped with balance in climbing, similar to some tree-living lizards with very long tails. Whether the last part of the tail was also prehensile is not discussed in the scientific description and so is speculation for now. The forelimbs are almost as long as the hindlimbs, but both pairs of legs are very short compared to the length of the trunk. The elements of the feet are enlarged, with elongated and slender digits. Distinct from other varanopids, the claws on Ascendonanus have a very strong curvature. The curved claws and the size and shape of the feet, including a longer fourth digit on the manus and on the pes, indicate Ascendonanus would have been a ″clinging″ climber rather than a ″grasping″ climber. A full description of the preserved integument of Ascendonanus has not been published yet. Current information indicates that the specimens show a regular scale pattern over their bodies, similar to living squamates and archosaurs, suggesting dry, scaly skin was present in the earliest amniotes before the split into synapsids and sauropsids (reptiles) during the Carboniferous Period. Some synapsid groups later developed bare, glandular skin, eventually with hair and whiskers that became characteristics of mammals.) Unlike some varanopids (such as Archaeovenator and Microvaranops), Ascendonanus does not have dorsal osteoderms on its upper trunk section along the back. However, the middle part of the tail has a covering of small scutes that continues to where the end of the tail is missing in all current specimens. The body outlines preserved show that Ascendonanus had a plump neck and muscular thighs (although the femur bone itself is relatively thin) on its short hindlimbs, while the trunk and the forelimbs are relatively slender. References Category:Varanopids Category:Fossil taxa described in 2018